Method and apparatus for determining velocity of moving objects



"M y ;1 1 YLPMACKTA 3,511,569

, METHOD AND 'Armm'rus FOR DETERMINING VELOCITY 0F MOVING OBJECTS Filedsept. 6. 1966 s Sheets-Sheet 1 FIG] F/GIZ IN VEN TOR. L E0 MAC K TAATTORNEY A MACKTA 3,511,569 METHOD 41 m APPARATUS FOR DETERMININGVELOCITY 0E MOVING OBJECTS Filed Sept. 6, .1966 s Sheets-Sheet z FIG. 4

IN VEN TOR. LEO MAC K TA AT ORNEY y 31970; AL. ,MACKTA 3,511,569

METHOD APPARATUS FOR DETERMINING VELOCITY F MOVING OBJECTS Filed Se t.6, 1966 s Sheets-Sheet a F IG. 7

FILTER RECTIFIER I I V /9e 2 2 we i 24a I /5e 2/6 {28 FILTER RECTIFIERINVENTOR. LEO MACKTA BY TTORNEY States Patent 3,511,569 METHOD ANDAPPARATUS FOR DETERMINING VELOCITY 0F MOVING OBJECTS Leo Mackta, 444Beach 132nd St., Belle Harbor, N.Y. Filed Sept. 6, 1966, Ser. No.577,458

Int. Cl. G0lp 3/36 ULS. Cl. 356-28 30 Claims This invention relatesgenerally to methods and apparatusifor determining the speed'of movingobjects. More particularly, it relates to the methods and apparatus fordetermining velocity by making and recording or reading hologramsofmoving objects.

his a known fact that a moving object will reflect beams of light ofvarying frequency. The frequency is changed in accordance with the wellknown Doppler shift. Further, by determining the change in frequency ofthe beam reflected by such object, one can determine the velocity ofsuch object.

One method for determining the shift or change in frequency of a beamreflected from a moving object is to direct a beam of known frequency atthe subject object and then measure or determine the frequency of thereflected jbeam. A laser or monochromatic beam of light, also referredto as coherent light, is a light source of determinable constantfrequency.

Asis already known, a hologram is a recording of the phase and amplitudepattern obtained when coherent light is reflected from or transmittedthrough an object and is caused to interfere with a reference beam ofcoherent light. The recording thus made contains all the informationnecessary for the reconstruction of the image ofwthe object, and thiscan be done by viewing the hologram in the illumination of coherentlight.

In the formation of a hologram, the reference light and the light fromthe object are generally from the same source, separated by prisms orpartially silvered mirrors, partially reflecting and partiallytransmitting, so thatthey are of the same frequency, and will thusproduce a stationary pattern to be recorded as the hologram.

Accordingly, it is an object of this invention to describe a means fordetermining the component of velocity of an objectin a radial directionfrom the observer, by means of altering the frequency of the referencelight during the formation of the hologram pattern. When the alteredreference frequency is the same as that reflected from the movingobject, a stationary hologram pattern will be obtained, while if the twofrequencies do not correspond, a blurring of the hologram will obtain sothat no sharp pattern will be formed.

Likewise, if the parts of an object are moving at different speedsrelative to the observer, as when in rotation, or. if. different objectsare moving at different speeds, a hologram pattern will be obtained onlyfor that part or that object which reflects light of a frequency whichis the same as that of the reference frequency. All the other parts orobjects will simply produce a constant background level of light overthe area of the hologram. Upon reconstruction of that image, only thoseparts or objects which were moving at the proper velocity would beobserved.

The: recording of the hologram may be made either photographically, onfilm, or, upon the sensitive cathode of a television type image orthicontube.

Accordingly, it is another object of this invention to provide a uniqueapparatus and highly advantageous method which will be extremelyversatile, being capable. of recording a hologram by various methods andapparatus.

Another important object of this invention is to provide ice a methodand apparatus for identifying an object moving at a specific or knownvelocity, thus to be able to select that object out of a background ofdifferent objects moving at different velocities.

It is a further object of this invention to provide a method andapparatus that may be used for determining the velocity of an objectwhich may be at a relatively short distance from the observer as well asfor determining the velocity of an object that may be at a relativelygreat distance from the observer.

It is another object of the present invention to provide apparatus ofthe type described which is relatively simple, thus obviating the needfor more complex and expensive equipment, and which will effectsubstantial savings in capital expenditure as well as in itsinstallation, maintenance and overhead costs.

It is a further object of the present invention to provide a uniquelyadvantageous method for determining the velocity of a moving object,which is capable of many varied applications, thus making it possible toachieve these objects by the use of relatively inexpensive equipment andwith an efliciency, accuracy and economy never before obtainable.

Other objects of the present invention will become apparent upon readingthe following specification and referring to the accompanying drawings,which form a material part of this disclosure.

The invention accordingly consists in the features of construction,combinations and arrangements of parts and method steps, which will beexemplified in the following description and of which the scope will beindicated by the appended claims.

In the drawings:

FIG. 1 is a diagrammatic representation of apparatus of the presentinvention, illustrating the practice of the instant method, forproducing a hologram of an object, on a photographic plate, with asingle source of coherent light;

FIG. 2 is a diagrammatic representation of apparatus of the presentinvention, illustrating an alternate embodiment for making a hologram,on a photographic plate, using two sources of coherent light;

FIG. 3 is a diagrammatic representation illustrating conceptually theappearance, under a normal light, of a hologram made by the apparatus ofeither FIG. 1 or 2;

FIG. 4 is a diagrammatic representation illustrating an alternateembodiment of the apparatus of FIG. 1 as employed in a method of theinvention for producing a series of holograms, at different frequenciesof the reference beam, on a single photographic plate;

FIG. 5 is a diagrammatic representation illustrating an alternateembodiment of the apparatus of FIG. 2 as employed in a method of theinvention for producing a series of holograms, at different frequenciesof the reference beam, on a single photographic plate;

FIG. 6 is a diagrammatic representation illustrating conceptually theappearance, under a normal light, of a hologram made with the apparatusof either FIG. 4 or 5;

FIG. 7 is a diagrammatic representation illustrating a furtherembodiment of the apparatus of either FIG. 1 or 4, in combination with atelevision image orthicon tube and other means as an alternate means forthe recording and reading of the hologram; and

FIG. 8 is a diagrammatic representation illustrating a furtherembodiment of the apparatus of either FIG. 2 or 5, in combination with atelevision image orthicon tube and an oscilloscope as an alternateapparatus for recording and reading the hologram.

Referring now more particularly to the drawings, and particularly toFIG. 1 thereof, there is illustrated therein apparatus for makingholograms of moving objects generally designated 10, including a sourceof coherent monochromatic light 11, a prism or partially silvered mirror13, means 14 for shifting the frequency of the reflected source beam, asecond prism or partially silvered mirror 15 and a photographic film orplate 16.

In the embodiment of FIG. 1, the components 11, 13, 14, 15 and 16 willeach be mounted in fixed relationship on a platform or other rigidmember (not shown) which may be moved about a variety of axes in orderto facilitate tracking of and aiming at the object which is to beholographed.

The beams of light 17 emitting from the source 11 will be directed atthe object (not shown) and will be partially reflected by and partiallytransmitted through the prism or partially silvered mirror 13. Thetransmitted beams 19 will continue along the path of the arrow 19 towardthe object and be reflected therefrom. Some of the reflected beams,returning along the path of the arrows 20, will be transmitted throughthe prism or partially silvered mirror 15 toward the photographic plate16. The beams reflected by the mirror 13 will proceed along the path ofthe arrow 21 toward the frequency shifting apparatus 14, by whichapparatus the said beams will be shifted in frequency, as desired. Thesaid frequency shifting apparatus will include means to increase thecrosssection and maintain the parallelism of the rays of the output beam17.

The frequency shifted beam will thence be directed along the path of thearrows 22 toward the mirror 15 to be thereby partially reflecteddownward toward the photographic plate 16. It is the combination of thebeam reflected from the object and transmitted through the mirror 15,and, the beam 22, reflected by the mirror 15, that produces the hologramon the photographic plate 16. This combination beam is designated 24.

The beams which are transmitted, through the mirror 13, toward theobject, along the path of the arrow 19, will be reflected from everypoint of the object toward every point on the photographic film 16.Likewise, the reflected portion 21 of the reference beam 17 Will beeventually reflected also to every point on the photographic plate.

If the frequency of the reflected beam is the same as that of thereference beam, then there will be areas of the photographic plate onwhich the wave fronts of beams are in phase and reinforce one another toproduce a stronger illumination, and, areas where the wave fronts of thebeams are 180 degrees out of phase so that they annul one another toproduce no illumination. For this condition of the same frequency forboth beams, these areas will constantly receive this reinforced andannulled illumination during the exposure period and the film will beexposed to this pattern. The resulting hologram will appear much likefingerprints, in an illegible pattern, as illustrated in FIG. 3. Thehologram thus produced may be read in a source of mono-chromatic light.

The light source 11 is a source of coherent mono-chromatic light and is,therefore, a source of constant frequency. Consequently, although therehas been a shift in the frequency of the beams 20 returning from theobject because of the Doppler shift, the frequency of the beams 21reflected by the mirror 13 will be constant. As a consequence, anycombination of the beams 20 and 21 will have no definite fixed relativephase over any portions of their wave fronts. In any small area of thephotographic film the illumination will alternate between bright anddark at a rate equal to the beat frequency, or the difference infrequency between the two beams. Therefore, for an exposure time whichpermits several cycles of this alternation to take place, any area ofthe film would have a uniform grey exposure. Therefore, a means isprovided for effecting a shift in the frequency of beam 21 so as toallow the two beams to produce a stationary pattern rather thanproducing the uniform graying of the film which would otherwise beproduced.

In the practice of this embodiment of the invention, the beam 21reflected by the mirror 13 will be shifted in frequency by the frequencyshifter 14 and a series of holograms made at different frequencies ofthe reference beam, that is, at different frequencies of the beam 22.The clearest image, that is, the clearest hologram, will be produced bya combination of beams Which are of the same frequency. Knowing,therefore, the frequency of the reference beam at which the clearesthologram was produced, one could determine the frequency of the beam 20reflected from the subject object and be thereby able to determine thevelocity of the subject object by any of the known methods forcalculating same.

The frequency shifter 14 is here illustrated merely diagrammatically. Itis understood, however, that the shifting in the frequency of a laser orcoherent light source may be accomplished by various known methods suchas parametric tuning. Another alternate apparatus that may be used forthe shifting of the frequency of the laser beam is a rotatingdiffraction grating such as that covered by my US. Pat. No. 3,267,284,dated Aug. 16, 1966.

The source 11 in FIG. 1 will generally be a continuous wave source.However,'the source 11 may, alternatively, be a pulsed source. That is,the source is actuated periodically to produce a pulsed beam or burst oflight.

There would, however, be a limitation where the subject object is at acomparatively great distance and the source of coherent light 11 is apulsed laser beam. More specifically, when the object is at a greatdistance, the pulsed beam may return from the object after the end ofthe pulsed time and, therefore, there will be little or no referencebeam with which to combine.

In the instance where the subject object is at a relatively greatdistance, there are two alternative arrangements.

The first alternative consists of using a low power pulsed laser, thatis, a beam of lesser intensity, as the light source 11 in FIG. 1, whichsource may be triggered at various delayed times, with reference to theinitiation of beam 19, so as to serve as the source for the beam thatwill be transmitted through the mirror 13 toward the object; and againtriggered at the proper time to be available as a source for thereference beam 22 to be combined with the beam 20 returning from thesubject object.

Another alternative is the use of the embodiment illustrated in the FIG.2 hereof.

Referring now to FIG. 2, there is illustrated therein an alternateembodiment of apparatus for making holograms of a moving object,generally designated 10a, including a source of coherent light 11a, asecond source of coherent light 12, means 14a for shifting the frequencyof the light from said second source, a prism or partially silveredmirror 15a and a photographic plate 16a.

In the embodiment of FIG. 2, the apparatus comprising the elements 11a,12, 14a, 15a and 16a will each be mounted in a fixed relation on a rigidplatform which may be moved or rotated about a variety of axes in orderto facilitate the tracking of or aiming at the subject object.

The light source 11a may be a high output continuous or pulsed laseremitting a beam of light along the direction of the arrow 19a, at afixed frequency, toward the subject object (not shown). The light source12 may be a continuous wave laser emitting a beam of light in thedirection of the arrow 21a toward a frequency shifter 14a. The beam 21awill be shifted in frequency by the shifter 14a and the frequencyshifted light beam 22a will be partially reflected and partiallytransmitted by the mirror 15a. The reflected portion of the beam 220will be reflected downward to combine on the photographic plate 16a,with the beam 20a returning from the subject object, thereby forming ahologram such as is illustrated in FIG. 3. It will thus be seen thathowever long a period of time is required for the beam, emitted from thesource 11a, to reach and return from the subject object, there willalways be a reference beam with which it may combine, thus to form aholograph of the subject object. The combined beam is designated 24a.

Itilwill also be recognized that the light source 12 may alternativelybe a low power pulsed laser that may be triggered at delayed intervalsto coincide with the time of the return of beam 20a reflected from thesubject object, thus to combine therewith to form a holograph of thesubject object.

Asin the embodiment of FIG. 1, a series of holograms will be made, atdifferent frequencies of the reference beam, and the frequency .of. thereflected beam 20a determined by noting the frequency of the referencebeam 22a whereby the clearest hologram was produced.

Itllwill berecognized, here also, that the shifting in frequency of thereference beam 21a may be accomplished byany of the previously mentionedmethods. In addition, inthe alternate embodiment of FIG. 2, the source12 and the frequency shifter 14a may be substituted by a source ofmono-chromatic light such as a ferrite laser that may be tuned, orfrequency shifted, internally as by a magnetic field.

Anotherapplication for the apparatus of FIGS. 1 and 2 would be toidentify an object moving at a specific or known velocity, that is, topick it out from a background of different objects moving at differentvelocities. This may be accomplished by setting the frequency of thereference beam at a value corresponding to the object velocity. Onlythat object which Was moving at a velocity corresponding to thefrequency of the reference beam will produce a sharp stationary patternon the holograph thus produced.

In another alternate embodiment of this invention the method andapparatus of FIGS. 1 and 2 may be supplemented by scanning the area ofthe hologram recording surface while the frequency of the referenceillumination is being varied. The recording surface, which may be aphotographic film or plate or photoelectric, is covered or shielded fromthe beams of light except for a narrow slitthrough which theillumination may pass through. The slit is swept across the recordingsurface in the manner. of the well known focal plane shutter, duringwhich period the frequency of the reference illumination is ,variedthrough a range of frequencies. Under these circumstances, where therecording surface is a photographic film, a thin line of holographicdetail will be obtained where the relative radial velocity of the objectis such that the Doppler shifted returned illumination corresponds infrequency to that of the reference illumination. Elsewhere on the filmthere will be a uniform grey, for a reasonable exposure time, asillustrated in FIG. 6.

Since, every portion of the hologram has sufficient information for thereproduction of an image of the object; a degraded image of the objectmoving with the indicated velocity may be reconstructed, from theappropriate velocity lineon the hologram, by viewing with monochromaticlight. Objects moving with different velocities could be reconstructedfrom different lines.

Referring now, more specifically, to FIG. 4, there is illustratedtherein an alternate embodiment of the apparatus of FIG. 1, generallydesignated 10b, including a source of coherent monochromatic light 11b,a prism or partially silvered mirror 13b, means 14b for shifting thefrequency of the reflected source beam, a second prism or partiallysilvered mirror 15b, a shutter or shield 18 and a photographic plate16b;

The components 11b, 13b, 14b, 15b, 18 and 16b will each be mounted in afixed relation on a platform or other rigidmember (not shown) which maybe moved about a variety of ,axes in order to facilitate tracking of andaiming at the object which is to be holographed.

As in theembodiment of FIG. 1, the source beam 17b Will be partiallyreflected by and partially transmitted through the mirror 13b. Thetransmitted beam 19b will be directed toward the object (not shown).Some of the beam 201;, reflected by the object, will be transmittedthrough the mirror 15b to be partially blocked from and partiallytransmitted, through the slit 23 of shield 18, toward the photographicplate 16b. The beams 21b reflected by the mirror 13b will be shifted infrequency, as desired, by the frequency shifter 14b. The frequencyshifted beam 22b will be partially reflected downward and likewisepartially blocked from and partially transmitted, through the slit 23 ofshield 18, toward the plate 16b.

As stated previously, the shield 18 may be a focal plane shutter, or, asillustrated, it may be any suitable shield having a slit 23 and meansfor a relative movement be tween the shield 18 and the plate 16b.

The hologram thus produced will appear as illustrated in FIG. 6.

An alternate embodiment of the apparatus of FIG. 2 is illustrated inFIG. 5. Referring now to FIG. 5, there is illustrated therein analternate embodiment for making holograms of a moving object, generallydesignated 10c, including a source of coherent light 11c, a secondsource of coherent light 120, means 14c for shifting the frequency ofthe light from said second source, a prism or partially silvered mirror15c, a shutter or shield 18c and a photographic plate 160.

The apparatus 10c will be mounted on a platform which may be moved orrotated to facilitate tracking of or aiming at the subject object.

As in the preceding embodiment of FIG. 2, the light source will be ahigh output laser directing a beam 19c at a fixed frequency, toward thesubject object (not shown). .The light source 12c will be a continuouswave laser emitting a beam 210 which will be shifted in frequency, asdesired, by the shifter 14c. The frequency shifted beam 220 will bepartially reflected by and partially transmitted through the mirror 15c.The reflected portion of the beam 22c will combine with the beams 20creflected from the object and transmitted through the mirror 15c. Thecombined beams 24c will be partially blocked from plate 16c by theshield or shutter 180. A holograph, as illustrated in FIG. 6, will beproduced on the plate 16c by the combined beams 240 that will passthrough the opening 23c of the shield as the plate and shield are movedrelatively.

The embodiments of the apparatus of FIGS. 1 and 2 relate to a method ofthis invention consisting basically of taking a series of holographs, insequence, each graph at a slightly different frequency of the referencebeam. The clearest, or that graph which reconstructs the clearest viewof the subject object, is determined by visual inspection. Thecorresponding frequency of the reference beam under which that graph wasmade is converted into relative radial velocity of the subject to thestation. This may be determined by the formula:

where:

The recording surface of FIGS. 1 and 2 is a photographic plate. In thealternative the holographic image may be recorded upon the sensitivecathode of a television type image orthicon tube.

For rapid determination of the velocity of an object, the mosaic of theimage orthicon tube is scanned by the electron beam in the conventionalmanner, although perhaps at a different rate. The electrical output ofthe tube may be modified by appropriate filter, rectified, and thenintegrated for an appropriate period, and the magnitude of the outputobserved. The formation of a stationary image on the photocathode willcause a maximum output to be observed. By correlating this maximumoutput with the corresponding frequency of the reference illumination,the Doppler shifted frequency reflected from the object and consequentlythe component of its velocity in a direction radial to the observer, maybe determined.

Referring now more particularly to FIG. 7, there is illustrated thereinan alternate embodiment of apparatus for determining the velocity ofmoving objects, generally designated 10d, including a source ofmonochromatic light 11d, a prism or partially silvered mirror 13d, means14d for shifting the frequency of the reflected source beam, a secondprism or partially silvered mirror 15d, an image orthicon tube 30, afilter 31 to modify the electrical output of the tube, a rectifier 32 torectify and integrate the output and a meter 33 to observe the magnitudeof the output.

The entire apparatus will be suitably mounted for tracking and aiming atthe subject object.

Further, it will be apparent that the mirror 13d may be replaced, as inthe embodiment of FIG. 2, by a second source of coherent light.

As in the embodiment of FIG. 1, the source beam 17d will be partiallyreflected by and partially transmitted through the mirror 13d. Thetransmitted beam 19d will be directed toward the object (not shown). Thebeam 21d reflected by the mirror 13d will be shifted in frequency, asdesired, by the frequency shifter 14d. The frequency shifted beam 22dwill be partially reflected by and partially transmitted through themirror 15d. The reflected portion of the beam 220! will combine with thebeam 20d reflected from the object and transmitted through the mirror15a. The combined beams 24d will be recorded by the image orthicon tube30 and the electrical output of the tube filtered, rectified andintegrated, by means of a filter 31 and rectifier 32, as aforesaid, andthe output observed on the meter 33. In practice, the frequency is setat a fixed value. The tube is scanned and a reading made. This processis repeated at various frequencies of the reference beam, and themaximum reading noted.

The embodiments of the apparatus of FIGS. 4 and relate to a secondalternate method of this invention, providing basically for theadditional step of scanning the area of the hologram recording surfacewhile the frequency of the reference illumination is being varied. Inthe embodiments of FIGS. 4 and 5, the recording surface comprises aphotographic plate. In the alternative, the recording surface may bephotoelectric mosaic array. If the recording surface is a photoelectricmosaic array (i.e. a television image orthicon tube), the mosaic may bescanned electronically in the conventional manner, with the fasterscanning rate in a direction parallel to the shutter slit. The scanningmay be performed at the same time as the exposure of the mosaic or atsome later time.

The output of the image orthicon tube is filtered and rectified and themaximum value displayed simultaneously with the indication of the amountof deflection of the slow scan. The deflection of the slow scancorresponds to a position of the shutter slit, which in turn willindicate the radial velocity of the object as heretofore explained inthe case where a photographic plate is used as the recording surface.

Referring now to FIG. 8, there is illustrated therein another alternateembodiment of apparatus for determining the velocity of moving objects,generally designated c, including a source of coherent light He, atsecond source of coherent light 12e, means 142 for shifting thefrequency of the light from said second source, a prism or partiallysilvered mirror e, a shutter or shield 18e, means 34 to actuate saidshield, an image orthicon tube 302, a filter 31e, a rectifier 322 and anoscilloscope 35.

The entire apparatus 10e will be suitably mounted for tracking andaiming at the subject object.

Further, it will be apparent that the second source of coherent light Hemay be replaced, as in the embodiment of FIG. 4, by a prism or partiallysilvered mirror.

As in the embodiment of FIG. 5, the light source He will be a laserdirecting a beam 19s, of fixed frequency, toward the object (not shown).The light source 12e will be a continuous wave laser emitting a beam 21ewhich may be shifted in frequency, as desired, by the frequency shifter142. The frequency shifted beam 22e will be partially reflected by andpartially transmitted through the mirror 15:2. The reflected portion ofthe beam 22e will combine with the beam 20:: reflected from the objectand transmitted through the mirror 15e. The combined beams 24e will bepartially blocked from the tube 30:? by the shield 182. A portion of thebeam 242 will be transmitted through an opening or slit 23a in theshield 18a and picked up by the tube 30e.

The tube scanner will be synchronized with the shutter or shieldactuator 34 and the frequency shifter 14e so that scanning of the tube30e and the rate of travel of the slit 232 relative the tube and therate of change in frequency of the reference beam will be insynchronization. The recorded image is filtered and rectified and willbe indicated on the oscilloscope, 35, the horizontal deflection of whichis a measure of the frequency of the reference beam 22e.

More particularly, the electrical output of the vertical deflection orslower scanning rate of the image orthicon tube 302 is connected at 40to a synchronization line 41 which is connected at 42 to the shieldactuator 34, at 43 to the frequency shifter 14c and at 44 to the sweepof the oscilloscope 35.

The horizontal or faster scanning rate of the tube 30s is utilized toscan the mosaic to determine a pattern. The output of the image orthicontube is fed through the filter 31e and the rectifier 322 to theoscilloscope 35 and will thus produce the vertical deflection on theoscilloscope image.

The oscilloscope image will move horizontally and be simultaneouslyvertically deflected by the output of the tube 30e thus producing apattern as at 45. The face of the oscilloscope may be calibrated as at46, to indicate, along the horizontal axis, the corresponding frequencyof the reference beam 22e. Visual inspection of the oscilloscope imagewill permit a determination of the peak 47 of the wave pattern 45. Thepeak 47 will be produced by the sharpest holographic image.Consequently, the frequency of the reference beam at which the sharpestimage was produced may be determined by reference to the calibrations46. The velocity, in a radial direction, of the subject may then bedetermined by the formula previously set forth or by the example belowset forth.

EXAMPLE Calculation of the Doppler frequency shift to be expected iscomputed as follows. The change in frequency A) is obtained forradiation scattered back from an object moving with a relative radialvelocity v.

Af=2v/L where:

L=wave length of the radiation used. v=velocity in centimeters persecond.

For purposes of calculation it is assumed that the wavelength is 5 10-cm., but any other may be used.

For example, miles per hour is approximately 5000 cm./sec., equivalent.to a frequency shift of 200 million cycles per second.

The velocity resolution obtainable is approximately proportional to theexposure time of the holograph, the longer the exposure, the better theresolution. Assume many objects with a wide range of relative radialvelocities for which a holograph is being made. The shifted referencefrequency used in making the holograph corresponds to the frequencyreceived from a particular object of the group, and for this object asharp stationary pattern is obtained on the recording surface. For otherfrequencies of radiation received from objects moving with differentradial velocities, the pattern which forms on the recording surfacealternates with time so that the light partsbecome dark and the darkparts become light. This happensat a rate which is the difference infrequency between the reference beamand the received beam.

Consider that this frequency difference is 40,000 cycles per, second,which for the formula given above for A), corresponds to a relativeradial velocity of 1 cm./sec. If thereference frequency correspondedwith some velocity of one of the objects of the group, then anotherobject moving with a relative radial velocity which is 1 cm. per secondfaster or slower, would cause its pattern on the recording surface toalternate 40,000 times per second. While the stationary pattern is beingsharply impressed optically on the recording surface, the pattern fromthe object: moving faster or slower is alternating, so that it producesonly a constant background level of illumination superimposed over thesharp pattern.

If. the exposure time for the holograph is .001 second, the pattern fromthe object moving 1 cm./sec. faster or slower will alternate 40 times,while that from the object moving with a velocity corresponding to thereference frequency will remain sharp throughout the exposure. Anexposure one-fourth as long will still produce alternations, adequate toblur out the undesired pattern, since in the Worst case the relativeexposures of the desired pattern to the one which is not wanted, is10:1.

Since the object whose relative radial velocity is to be determined mayalso have a transverse component of velocity, it is necessary for theapparatus used in the radial velocity measurement to be pointed at theobject by a tracking mechanism. Such tracking mechanisms, either manualor automatic, are well known in the field, and may be incorporated inthe mounting base of the velocity measuring apparatus by any well-knownmeans.

From the foregoing, it is seen that the present invention provides amethod and apparatus for determining the velocity of moving objects,which fully accomplish their intended. objects and are Well adapted tomeet practical conditions of manufacture and use.

Although the present invention has been described in some detail by wayof illustration and example for purposes of clarity of understanding, itis understood that certain changes and modifications may be made withinthe, spirit of the invention and scope of the appended claims.

What is claimed is:

1. Method for determining the velocity of a moving object, comprisingthe following steps: directing a. first source of monochromatic light ofconstant frequency toward the object, the velocity of which is to bedeter mined; combining the beams of monochromatic light from said firstsource, reflected by said object, with a second reference source ofmonochromatic light of varying. frequency; exposing said combined beamsto the surface of a photo-sensitive receptor; and reading the resultantimages to determine the clearest image produced as a result of thesynchronization of the frequencies of the reference source and thereflected light, thus, to determine the relative radial velocity of saidobject to said first source.

2. The method of claim 1 further including the step of? varying thefrequency of said reference source prior to combining. said reference.source with said beams from said first source reflected by said object.

3. The method of claim 2 further including the steps of: making a seriesof holograms of said object, from said combined beams, at differentfrequencies of the reference source; and, comparing said series ofholograms.

4. The method of claim 2 further including the steps of: partiallyshielding a photographic film, to be exposed to said combined beams,from said combined beams; and, synchronously moving, relatively, saidphotographic film and, said shielding so as to produce on said film aseries of holographic images of said object at different frequencies ofsaid reference source.

5. The method of claim 2 further including the steps of: exposing saidcombined beams to a photoelectric mosaic array; electronically scanningthe input to said photoelectric mosaic array; filtering and rectifyingthe output from said photoelectric mosaic array; and indifating theresultant electronic image on a meter or the ike.

6. The method of claim 2 further including the steps of: partiallyshielding said combined beams from a photoelectric mosaic array, andpartially exposing said combined beams to said photoelectric mosaicarray; electronically scanning the input to said photoelectric mosaicarray; synchronizing the exposure of said combined beams across the faceof said photoelectric mosaic array with the rate of said scanning;filtering and rectifying the output from said photoelectric mosaicarray; and indicating the resultant electronic image on an oscilloscopeor the like.

7. Method for determining the velocity of a moving object comprising thefollowing steps: directing a source of monochromatic light, of constantfrequency, toward the object, the velocity of which is to be determined;partially reflecting and partially transmitting the beam from saidsource of monochromatic light, said transmitted portion of said beambeing directed toward said object, said reflected portion serving as areference beam; varying the frequency of said reference beam; combiningthe said transmitted portion of the beam of monochromatic lightreflected by said object with the frequency shifted reference beam;exposing said combined beams to the surface of a photo-sensitivereceptor; and reading the resulting images to determine the clearestimage produces as a result of the synchronization of the frequencies ofthe reflected beam and the reference beam, thus, to determine therelative radial velocity of said object to said source.

8. The method of claim 7 further including the steps of: making a seriesof holograms of said object from said combined beams at differentfrequencies of the reference beam; and comparing said series ofholograms.

9. The method of claim 7 further including the steps of: partiallyshielding a photographic film, to be exposed to said combined beams,from said combined beams; and synchronously moving, relatively, saidphotographic film and said shielding so as to produce on said film aseries of holographic images of said object at different frequencies ofthe reference beam.

10. The method of claim 7 further including the steps of: exposing saidcombined beams to a photoelectric mosaic array; electronically scanningthe input to said photoelectric mosaic array; filtering and rectifyingthe output from said photoelectric mosaic array; and indicating theresultant electronic image on a meter or the like.

11. The method of claim 7 further including the steps of: partiallyshielding said combined beams from a photoelectric mosaic array, andpartially exposing said combined beams to said photoelectric mosaicarray; electrom'cally scanning the input to said photoelectric mosaicarray; synchronizing the exposure of said combined beams across the faceof said photoelectric mosaic array with the rate of said scanning;filtering and rectifying the output of said photoelectric mosaic array;and recording the resultant electronic image on an oscilloscope or thelike.

12. Method for identifying an object moving at a known velocitycomprising the following steps; directing a first source ofmonochromatic light of constant frequency toward the object to beidentified, said frequency corresponding to the velocity of said object;combining the beams of monochromatic light, from said first source,reflected by said object and other surrounding objects, with a secondreference source of monochromatic light of a fixed known frequency;exposing said combined beams to the surface of a photo-sensitivereceptor; and reading the resultant image, to determine the clearestobject image produced as a result of the synchronization of thereference source and the reflected light, thus, to distinguish theobject to be identified from other objects moving at differentvelocities.

13. Method for identifying an object moving at a known velocity,comprising the following steps: directing a source of monochromaticlight, of constant frequency, toward the object to be identified, saidfrequency corresponding to the velocity of said object; partiallyreflecting and partially transmitting the beam from said source ofmonochromatic light, said transmitted portion of said beam beingdirected toward said object, said reflected portion serving as areference beam; combining the said transmitted portion of said sourcebeam, reflected by said object and other surrounding objects, with thesaid reference beam; exposing said combined beams to the surface of aphoto-sensitive receptor; and reading the resultant image, to determinethe clearest image produced as a result of the synchronization of thefrequencies of the reference source and the reflected light, thus, todistinguish the object to be identified from other surrounding objectsmoving at different velocities.

14. Apparatus for determining the velocity of moving objects,comprising: a first source of monochromatic light of constant frequency;means to direct the beam from said first source toward the object, thevelocity of which is to be determined; a second reference source ofmonochromatic light of variable frequency; means to transmit the beamemanating from said first source and reflected by said object, and toreflect the beam from said reference source thus to facilitate thecombining of said beams; a photo-sensitive receptor; means to exposesaid combined beams to said photo-sensitive receptor to determine theclearest image produced as a result of the synchronization of thefrequencies of the reference source and the reflected light; and meansfor tracking the object, the velocity of which is to be determined; allof said components being mounted in adjustable fixed relationship tosaid tracking means.

15. Apparatus for determining the velocity of moving objects, accordingto claim 14; further including means, positioned between said referencesource and said means for transmitting and reflecting light beams, forvarying the frequency of said reference source; and wherein saidreference source is a source of constant frequency.

16. Apparatus for determining the velocity of moving objects, accordingto claim 15; wherein said photo-sensitive receptor is a photographicplate.

17. Apparatus for determining the velocity of moving objects, accordingto claim 16; further including means for partially shielding from andpartially exposing; said combined beams, to said photographic plate.

18. Apparatus for determining the velocity of moving objects, accordingto claim 17; further including means for synchronizing the exposure, ofportions of said photographic film to said combined beams, with the rateof change of frequency of said reference source beam.

19. Apparatus for determining the velocity of moving objects, accordingto claim 15; wherein said photo-sensitive receptor is a photoelectricmosaic array.

2.0. Apparatus for determining the velocity of moving objects, accordingto claim 15; wherein said photo-sensitive receptor is an image orthicontube; and further including means to modify the output of said tube;means to rectify and integrate the said output; and means to observe themagnitude of said output.

21. Apparatus for determining the velocity of moving objects, accordingto claim 20; further including means for scanning said tube; means forsynchronizing the exposure, of portions of said image orthicon tube tosaid combined 12 beams, with the rate of scanning of said tube and therate of change of frequency of 'said reference source beam.

22. Apparatus for determining the velocity of moving objects,comprising: a source of monochromatic light, of constant frequency;first means for partially reflecting and partially transmitting the beamfrom said source, the transmitted portion of said beam being directedtoward the object, the velocity of which is to be determined, thereflected portion of said source beam serving as a reference beam; meansfor varying the frequency of said reference beam; second means totransmit the beam transmitted by said first means for reflecting andtransmitting, and, to reflect the frequency-shifted reference beam, thusto facilitate the combining of said beams; a photo-sensitive receptor;means to expose said combined beams to said photo-sensitive receptor todetermine the clearest image produced as a result of the synchronizationof the reference beam and the reflected beam; and means for tracking thesaid object; all of said components being mounted in adjustable fixedrelationship to said tracking means.

23. Apparatus for determining the velocity of moving objects, accordingto claim 22; wherein said photo-sensitive receptor is a photographicplate.

24. Apparatus for determining the velocity of moving objects, accordingto claim 23; further including means for partially shielding from andpartially exposing, said combined beams, to said photographic plate.

25. Apparatus for determining the velocity of moving objects, accordingto claim 24; further including means for synchronizing the exposure, ofportions of said photographic film to said combined beams, with the rateof change of frequency of said reference source beam.

26. Apparatus for determining the velocity of moving objects, accordingto claim 22; wherein said photo-sensitive receptor is a photoelectricmosaic array.

27. Apparatus for determining the velocity of moving objects, accordingto claim 22; wherein said photo-sensitive receptor is an image orthicontube; and further including means to modify the output of said tube;means to rectify and integrate the said output; and means to observe themagnitude of said output.

28. Apparatus for determining the velocity of moving objects, accordingto claim 27; further including means for scanning said tube; means forsynchronizing the exposure, of portions of said image orthicon tube tosaid combined beams, with the rate of scanning of said tube and the rateof change of frequency of said reference source beam.

29. Apparatus for identifying an object moving at a known velocity,according to claim 16.

30. Apparatus for identifying an object moving at a known velocity,according to claim 23.

References Cited UNITED STATES PATENTS 3,267,284 8/1966 Mackta.3,284,799 11/1966 Ross. 3,409,369 11/1968 Bickel 356--28 OTHERREFERENCES G. Bierson et al.: Requirements of a Coherent LaserPulse-Doppler Radar, July 2, 1962, Proceedings of the IEEE, pp. 202-209.

B. P. Hildebrand et al.: Interferometric Measurements Using WaveformsReconstruction Technique, January 1966, Applied Optics, vol. 5, No. 1,pp. 172-173.

RODNEY D. BENNETT, JR., Primary Examiner J. P. MORRIS, AssistantExaminer

1. METHOD FOR DETERMINING THE VELOCITY OF A MOVING OBJECT, COMPRISING THE FOLLOWING STEPS; DIRECTING A FIRST SOURCE OF MONOCHROMATIC LIGHT OF CONSTANT FREQUENCY TOWARD THE OBJECT, THE VELOCITY OF WHICH IS TO BE DETERMINED; COMBINING THE BEAMS OF MONOCHRMATIC LIGHT FROM SAID FIRST SOURCE, REFLECTED BY SAID OBJECT, WITH A SECOND REFERENCE SOURCE OF MONOCHROMATIC LIGHT OF VARYING FREQUENCY; EXPOSING SAID COMBINED BEAMS TO THE SURFACE OF A PHOTO-SENSITIVE RECEPTOR; AND READING THE RESULTANT IMAGES TO DETERMINE THE CLEAREST IMAGE PRODUCED AS A RESULT OF THE SYNCHRONIZATION OF THE FREQUENCIES OF THE REFERENCE SOURCE AND THE REFLECTED LIGHT, THUS, TO DETERMINE THE RELATIVE RADIAL VELOCITY OF SAID OBJECT TO SAID FIRST SOURCE. 